Resonant hair humidity sensors for disposable applications: Revisit the hair hygrometer

Yoon, Yeowon,Thundat, Thomas,Lee, Jungchul Elsevier 2019 Sensors and actuators. B Chemical Vol.292 No.-

<P><B>Abstract</B></P> <P>Hairs have long been used for humidity sensing with the aid of their unique property, elongation upon the increase of ambient humidity. However, relatively long strands of hairs are required to induce measurable length change. While such long strands of hairs amplify the readout signal, they, in turn, compromise the spatiotemporal resolution. Here, we revisit the hair hygrometer, firstly demonstrated by a Swiss physicist and geologist, Horace Bénédict de Saussure in 1783, by making suspended string resonators with a short segment of human hairs. A short segment of human hair is placed onto a substrate with a through-hole and then firmly fixed under tension to make a taut suspended string. As a final step, a thin gold layer is locally deposited onto the suspended hair through a shadow mask. While the prepared hair resonator is driven by a piezo actuator, its resonance frequency is optically measured. Measurements confirm that the resonance frequency of the hair resonator decreases as the relative humidity increases. The water absorption decreases both the tension and the stiffness of the hair resonator and increases the inertial mass of the hair resonator, all of which contribute to the reduction of the resonance frequency.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We report a new method for humidity measurements by using human hairs. </LI> <LI> A short segment of a single strand of hair mounted on a machined jig simply constitutes a mechanical resonator. </LI> <LI> The hair resonator offers high spatial and temporal resolutions with the aid of its miniaturized dimension. </LI> <LI> Historical hair hygrometers are successfully revisited with improved performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fluidic applications for atomic force microscopy (AFM) with microcantilever sensors

Kim, Seonghwan,Kihm, Kenneth D.,Thundat, Thomas Springer-Verlag 2010 Experiments in fluids Vol.48 No.5

Rapid discrimination of DNA strands using an opto-calorimetric microcantilever sensor.

Lee, Dongkyu,Hwang, Kyo Seon,Kim, Seonghwan,Thundat, Thomas Royal Society of Chemistry 2014 Lab on a chip Vol.14 No.24

<P>A rapid technique for quantitative detection and discrimination of DNA strands without using immobilized probe molecules is demonstrated using an opto-calorimetric, self-powered sensor based on a Pb(Zr(0.52)Ti(0.48))O3 (PZT) microcantilever. Microcalorimetric infrared (IR) spectroscopy provides excellent chemical selectivity based on the unique molecular vibrational characteristics of each nucleotide in the mid IR region. The piezoelectric and pyroelectric properties of the PZT microcantilever were exploited in the quantitative detection and discrimination of adsorbed DNA strands with their spectral characteristics. We report the unique spectral characteristics of different DNA nucleotides that are monitored by wavelength-dependent temperature variations for different relative molar ratio of each nucleotide. This approach offers a fast, label-free technique which is highly sensitive and selective for the detection of single nucleotide differences in DNA strands and has the potential to be used as a rapid prescreening biosensor for various biomolecules.</P>

Effects of gold patterning on the bending profile and frequency response of a microcantilever

Lee, Dongkyu,Kim, Seonghwan,Jung, Namchul,Thundat, Thomas,Jeon, Sangmin American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.106 No.2

Direct Detection and Speciation of Trace Explosives Using a Nanoporous Multifunctional Microcantilever

Lee, Dongkyu,Kim, Seonghwan,Jeon, Sangmin,Thundat, Thomas American Chemical Society 2014 ANALYTICAL CHEMISTRY - Vol.86 No.10

<P>We have developed a highly selective and sensitive nanomechanical infrared (IR) calorimetric spectrometer for use in the direct detection of ultralow concentrations of explosive vapors using a nanoporous TiO<SUB>2</SUB> cantilever. These cantilevers were fabricated using a two-step anodization and photolithography process. By patterning nanoscale wells onto a cantilever, its surface area is increased by 2 orders of magnitude and the surface is converted into a preconcentrator. Resonant excitation of adsorbed molecules using IR radiation causes the cantilever to bend due to temperature changes originating from the nonradiative decay process. The porous structure of the cantilever increases its thermomechanical sensitivity as well as the number of adsorbed molecules. The system performance was demonstrated by detecting binary explosive mixtures under ambient conditions. The TiO<SUB>2</SUB> sensor surface also allows regeneration through the photocatalytic decomposition of adsorbates under UV irradiation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2014/ancham.2014.86.issue-10/ac500745g/production/images/medium/ac-2014-00745g_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac500745g'>ACS Electronic Supporting Info</A></P>

Electronic Nose for Recognition of Volatile Vapor Mixtures Using a Nanopore-Enhanced Opto-Calorimetric Spectroscopy

Chae, Inseok,Lee, Dongkyu,Kim, Seonghwan,Thundat, Thomas American Chemical Society 2015 ANALYTICAL CHEMISTRY - Vol.87 No.14

<P>An electronic nose (e-nose) for identification and quantification of volatile organic compounds (VOCs) vapor mixtures was developed using nanopore-enhanced opto-calorimetric spectroscopy. Opto-calorimetric spectroscopy based on specific molecular vibrational transitions in the mid infrared (IR) “molecular fingerprint” regime allows highly selective detection of VOCs vapor mixtures. Nanoporous anodic aluminum oxide (AAO) microcantilevers, fabricated using a two-step anodization and simple photolithography process, were utilized as highly sensitive thermomechanical sensors for opto-calorimetric signal transduction. The AAO microcantilevers were optimized by fine-tuning AAO nanopore diameter in order to enhance their thermomechanical sensitivity as well as their surface area. The thermomechanical sensitivity of a bilayer AAO microcantilever with a 60 nm pore diameter was approximately 1 μm/K, which is far superior to that of a bilayer plain silicon (Si) microcantilever. The adsorbed molecules of VOCs mixtures on the AAO microcantilever were fully recognized and quantified by variations of peak positions and amplitudes in the opto-calorimetric IR spectra as well as by shifts in the resonance frequency of the AAO microcantilever with the adsorbed molecules. Furthermore, identification of complex organic compounds with a real industrial sample was demonstrated by this e-nose system.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2015/ancham.2015.87.issue-14/acs.analchem.5b00915/production/images/medium/ac-2015-00915q_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac5b00915'>ACS Electronic Supporting Info</A></P>

Nanomechanical Thermal Analysis of Photosensitive Polymers

Yun, Minhyuk,Yim, Changyong,Jung, Namchul,Kim, Seonghwan,Thundat, Thomas,Jeon, Sangmin American Chemical Society 2011 Macromolecules Vol.44 No.24

<P>A few nanograms of poly(methyl methacrylate) (PMMA) or poly(vinyl cinnamate) (PVCN) was coated onto one side of a silicon cantilever, and the photodegradation of PMMA or photo-cross-linking of PVCN was investigated as a function of UV irradiation time. After UV irradiation, the resonance frequency and deflection of the polymer-coated silicon cantilevers were measured as a function of temperature, and these properties were found to be related to changes in the modulus and surface stress of the coated polymers, respectively. A decrease in the modulus and tensile surface stress was observed for PMMA under UV exposure due to photodegradation, whereas an increase in the modulus of PVCN was observed due to photo-cross-linking. In addition, the influence of UV exposure on the glass transition of the PMMA and PVCN was investigated using deflection measurements. Whereas a single glass transition was observed for PMMA, two distinctive glass transitions were observed for PVCN due to the copresence of cross-linked and un-cross-linked of PVCN. Variations in the polymer structures were also investigated as a function of UV irradiation time using Fourier transform infrared spectroscopy and compared with the results obtained using the cantilever measurements.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2011/mamobx.2011.44.issue-24/ma202194e/production/images/medium/ma-2011-02194e_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma202194e'>ACS Electronic Supporting Info</A></P>

Heat capacity measurements of sub-nanoliter volumes of liquids using bimaterial microchannel cantilevers

Khan, M. F.,Miriyala, N.,Lee, J.,Hassanpourfard, M.,Kumar, A.,Thundat, T. American Institute of Physics 2016 Applied Physics Letters Vol.108 No.21

Nanowell-patterned TiO₂ microcantilevers for calorimetric chemical sensing (5 pages)

Lee, D.,Kim, S.,Chae, I.,Jeon, S.,Thundat, T. American Institute of Physics 2014 Applied Physics Letters Vol.104 No.14

Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS₂ multilayers

Liu, Jun,Goswami, Ankur,Jiang, Keren,Khan, Faheem,Kim, Seokbeom,McGee, Ryan,Li, Zhi,Hu, Zhiyu,Lee, Jungchul,Thundat, Thomas Nature Publishing Group UK 2018 Nature nanotechnology Vol.13 No.2

<P>The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting(1-3). A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification(2). Here, we show that continuous direct-current (d.c.) with a maximum density of 10(6) A m(-2) can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS2). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (105-106 V m(-2)) at the conductive nanoscale tip(4). We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current-voltage spectra analysis indicates that the rectifying Schottky barrier at the tip-sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.</P>